Nitrogen Rate and Timing Effects on Winter Wheat Grain Yield, Grain Protein, and Economics
1990
Typically, N fertilizer is fall-applied to dryland winter wheat (Triticum aestivum L.) in the Great Plains, because cheaper N sources (anhydrous ammonia) can be applied in the fall and application can be combined with seedbed preparation tillage. Spring- or split-applied N provides increased N management flexibility and potentially less N loss due to leaching or denitrifi-cation over the winter. This study was conducted to compare winter wheat grain yields, protein, and economic returns associated with fall-, spring-, and split-applied N at rates of 0, 20, 40, and 60 lb N/acre at 19 sites over 3 yr (1985–1987) in eastern Colorado. Grain yield response to N fertilizer was dependent on precipitation or residual soil NO₃ levels, while grain protein response was not. Spring-applied N increased grain yields and protein more than fall- and split-applied N. Fall-applied N required 20 and 18% (mean) more spring-applied N to achieve the same grain yield and protein content, respectively. Spring-applied N was more profitable than fall- or split-applied N. Without application cost (“free ride”), N applied to solely increase grain protein was profitable. In semiarid climates, spring-applied N is more available to winter wheat and more profitable than fall or split-applied N.
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